Many types of medical devices are used in a variety of medical procedures that include at least partial implantation into a body. When implanted, medical devices can be in intimate contact with a variety of cells, tissues, and body systems. For example, cannulae, such as catheters, are used in a variety of medical procedures to introduce articles, such as stents, into body vessels. Cannulae are also used to establish a communicative passageway by which a body vessel can be accessed from the exterior of the body. These cannulae are indispensable in procedures that require repeated access to the vessel, such as hemodialysis procedures that include repeated extracorporeal treatment of blood.
While implanted medical devices provide several advantages, they also present an opportunity for infection. Indwelling medical devices, such as indwelling cannulae used for access ports, are particularly susceptible to infection due to their long term presence in the body. In essence, the cannula provides a path from the external environment into the body along which microorganisms can colonize, and eventually produce an infection.
The establishment of an infection can require intervention, such as treatment with a therapeutic agent or even mechanical manipulation of the medical device to remove the microorganisms. Even worse, the infection may require removal and replacement of the medical device. Ultimately, the presence of an infection may outweigh the benefits of the implantation.
Infections associated with indwelling medical devices are commonly caused by bacteria or fungi. The most common organisms associated with infections associated with indwelling devices are Staphylococcus epidermidis and Staphylococci aureus. Candida albicans, a fungi, is another significant cause of infections associated with these devices. No matter the microorganism, establishment of infection requires colonization along the surface of the medical device, which depends on a variety of factors, including the formation of glycocalyx and a fibrin sheath.
Glycocalyx is a polysaccharide produced by adherent microorganisms. The glycocalyx allows the microorganisms to adhere to the surface, and contributes to the formation of a biofilm around the medical device. In addition to the glycocalyx formation, a fibrin sheath is often produced by the host as a natural result of thrombogenesis. The fibrin sheath essentially covers the surfaces of the indwelling device, and provides another agent onto which microorganisms can adhere.
Considering the importance of implantable medical devices, considerable attention has been directed toward preventing colonization and/or infection on these articles. The art contains many examples of medical devices that incorporate a variety of approaches that attempt to control colonization and/or infection. For example, U.S. Pat. No. 5,688,516 to Raad et al. discloses medical devices coated with mixtures of antibiotics and other therapeutic agents. Also, U.S. Pat. No. 5,624,704 to Darouiche et al. discloses medical devices impregnated with antimicrobials.
As indicated above, the microorganisms commonly associated with colonization and/or infection from implanted medical devices typically originate from outside the body, such as on the skin, and progress into the body along the path of the medical device. Once inside the body, the microorganisms produce the glycocalyx that facilitates adherence, and the body produces a fibrin sheath around the device that facilitates colonization and establishment of an infection. Thus, two distinct processes are occurring on two distinct portions of the medical device. Outside the body, microorganisms gain access to the device and begin to proceed into the body. Inside the body, microorganisms arriving from the external portion of the device produce a glycocalyx to facilitate adherence, and the body produces the fibrin sheath which further facilitates adherence. The prior art fails to recognize the localization of these processes in the available devices designed to prevent or inhibit colonization and/or infection.